1. Field of the Invention
The present invention relates to an imaging apparatus of an electronic endoscope for taking an image inside of the coelom, and an electronic endoscope including the imaging apparatus.
2. Description of Related Art
A medical diagnosis utilizing an electronic endoscope has been actively carried out in a medical field. A front end of an inserting portion of an electronic endoscope inserted into a coelom includes an imaging apparatus having a solid-state imaging device such as CCD and the like. An image inside of the coelom can be observed with a monitor by subjecting an imaging signal output from CCD to various signal processings by a processor apparatus.
The imaging apparatus includes the CCD mentioned above and an object optical system for taking in image light of an observed portion inside of the coelom, the image light being incident from an observation window provided at the front end of the inserting portion. A cover glass is arranged above an imaging surface (light receiving surface) of CCD to be spaced apart from each other therebetween by a gap (air gap).
Meanwhile, the front end of the inserting portion of the electronic endoscope inserted into the coelom is brought into a temperature to a degree the same as that of the physical temperature (about 37° C.). In contrast, a temperature inside of the inserting portion becomes higher than the physical temperature to be occasionally equal to or higher than 40° C. by heat of driving an electronic part of CCD or the like. In addition, there is a case of injecting cleaning water or air to the front end of the inserting portion when the observation window is stained, and therefore, a temperature difference is produced between a surface and the inner portion of the front end of the inserting portion. Therefore, when moisture is included inside of the inserting portion, there is a case in which dew condensation is produced on an object optical system or cover glass.
Particularly, an inner surface of the cover glass is proximate to an imaging surface of CCD, and therefore, a temperature thereof is liable to be high, on the other hand, there is a case in which an outer surface of the cover glass is rapidly cooled by injecting cleaning water or the like, and therefore, dew condensation is produced at an inner surface of the cover glass by moisture included in the air gap.
Further, in using an electronic endoscope which has been stored, when the electronic endoscope is connected to a processor apparatus and a power source is made ON, whereas a temperature of a solid-state imaging device rapidly rises immediately thereafter, a temperature of a member such as an object optical system and a cover glass gradually rises by receiving heat of the solid-state imaging device or a peripheral circuit. Therefore, immediately after making the power source ON, a temperature difference between the solid-state imaging device and the cover glass is large and dew condensation is liable to be produced.
Although when dew condensation is produced at the object optical system, a blurred image is simply brought about and an influence is not effected so much on observation, when dew condensation is produced on the inner surface of the cover glass as described above, the image quality is deteriorated considerably to a degree of being able to optically recognize water drops on an image and the observation becomes difficult. In view of such a background, various proposals have been made in order to prevent dew condensation of the inner surface of the cover glass (refer to JP-A-2003-284686).
JP-A-2003-284686 discloses an imaging apparatus of an electronic endoscope, in which a heat generating member such as a peripheral circuit of a solid-state imaging device is disposed at a vicinity of a cover glass to warm up an outer surface of the cover glass. JP-A-2003-284686 describes a first embodiment using only the peripheral circuit as a heat generating member, in addition, a second embodiment using a board extended substantially in a channel-like shape to surround the cover glass in three directions, and a third embodiment providing a heater in place of the peripheral circuit.
According to the invention described in JP-A-2003-284686, the peripheral circuit is mounted to the board. The board generally includes a material whose major component is alumina from reason of being inexpensive, easy to fabricate or the like. Generally, a heat conductivity of the board including the material whose major component is alumina is high, and therefore, heat of the peripheral circuit is escaped to a side of an operating portion on the hand side of the electronic endoscope by way of a wiring connected to the peripheral circuit. Therefore, even when a surface of the cover glass is intended to warm up by heat of the peripheral circuit, heat is not transferred efficiently to the surface of the cover glass. Therefore, according to the invention described in JP-A-2003-284686, it is necessary to use the extended board having a special shape or provide the heater, and hence fabrication cost and part cost are increased.